Water cannon

ABSTRACT

A system is disclosed for producing a pulsed liquid jet of high dynamic pressure using a shaped projectile propelled through a gun barrel into which a liquid has just been injected to form a hollow cylinder or cone. The projectile is shaped to accelerate the liquid inward toward the barrel axis resulting in the production of a jet at high velocity, either by changing the path of the liquid to one along the barrel axis in the direction of projectile motion by an annular cusp shape at the front end of the projectile, or by producing an implosion of the liquid by an essentially annular wedge shape of the projectile which forces the liquid to converge on the gun barrel axis almost instantaneously.

United States Patent 1191 Godfrey [451 July 31,1973

[ WATER CANNON [75] Inventor: Charles S. Godfrey, Berkeley, Calif.

[73] Assignee: Physics International Company, San

Leandro, Calif.

22 Filed: Sept. 15,1971

[21] App]. No.2 179,673

[52] U.S. Cl 89/1 R, 89/8, 239/101 [51] Int. Cl F4lf 1/00 [58] Field of Search 222/79; 89/8, 1; 239/ 101, 102

[56] References Cited UNITED STATES PATENTS 3,468,481 9/1969 Cooley 89/8 X 3,468,217 9/1969 Cooley 89/8 3,478,966 11/1969 Cooley 89/8 X 7/1970 Cooley 239/101 3,521,820 7/1970 Cooley 239/101 Primary Examiner-Samuel W. Engle Attorney-Lindenberg et a1.

[57] ABSTRACT A system is disclosed for producing a pulsed liquid jet of high dynamic pressure using a shaped projectile propelled through a gun barrel into which a liquid has just been injected to form a hollow cylinder or cone. The projectile is shaped to accelerate the liquid inward toward the barrel axis resulting in the production of a jet at high velocity, either by changing the path of the liquid to one along the barrel axis in the direction of projectile motion by an annular cusp shape at the front end of the projectile, or by producing an implosion of the liquid by an essentially annular wedge shape of the projectile which forces the liquid to converge on the gun barrel axis almost instantaneously.

PAIENIED 3.748.953

SHEET 2 BF 2 INVENTOR. 44 1 CHAQAES 5. GO

WATER CANNON BACKGROUND OF THE INVENTION ton would transmit its kinetic energy suddenly to a.

water reservoir having a nozzle. The result would be a water jet. In speaking of steady state flows, the stagnation pressure cannot exceed the internal chamber pressure in the reservoir. However, in speaking of unsteady expansion, it is well known that the lead portion of the expanding fluid can attain a higher total energy density than that of the reservoir. With proper nozzle design, for example, and using pressures in the reservoir not exceeding 60,000 psi, a jet having an initial stagnation pressure of up to 300,000 psi can be achieved. This stagnation pressure is equivalent to a velocity of about 6,000 ft/sec. Most of the flow in this case, however, is delivered at velocities less than 2000 ft/sec.

The requirement for creating a large reservoir capable of holding 60,000 psi implies large metal parts and special related hardware. The resultant device becomes expensive to build and, because of its weight and size, difficult to employ in an excavation tunnel, for example.

The present invention is capable of achieving much higher performance while employing peak pressures not exceeding 30,000 psi. A device embodying said invention would be lighter in weight and cheaper, both to build and to employ.

SUMMARY OF THE INVENTION In accordance with the present invention a shaped projectile is propelled through a gun barrel into which a liquid has been injected in the form of a ring (hollow cylinder or cone) just prior to launching the projectile. The projectile is shaped to scoop up the liquid, accelerate the liquid toward the axis of the gun barrel, resulting in the production of a jet at high velocity. In one embodiment, the liquid ring is injected in the form of a hollow cylinder on the inner surface of the gun barrel, and the projectile is shaped in the form of an annular cusp to accelerate the liquid inward and forward (i.e. in the direction of motion of the projectile) such that it forms an axial jet. In a second embodiment, the liquid ring is injected in the form of a hollow frustrum of a cone, and the projectile is shaped in the form of an annular wedge to accelerate the liquid cone inward, thereby producing an implosion of the liquid which produces a jet in the direction of the projectile motion. Stress on the projectile from the formation of the liquid jet is reduced by shaping the projectile with an axial passage of a diameter which decreases at a non-linear rate from the front to the rear, starting with a diameter at the front substantially equal to the external diameter of the projectile.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a projectile being propelled in a gun barrel to form a liquid jet according to the present invention from a hollow cylinder of liquid in the gun barrel.

FIG. 2 shows a portion of the sectional view of FIG. 1 enlarged to illustrate a feature of the projectile.

FIG. 3 is a graph of velocity and kinetic energy of the projectile of FIG. 1 and liquid as a function of the distance of travel of the projectile.

FIGS. 4a to 4d illustrate schematically a second embodiment of the present invention and, in the successive figures, the progression of a virtual implosion of a hollow liquid frustrum of a cone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a copending application, Ser. No. 24,562, titled Rock. Fracturing Method and Apparatus for Excavation filed Apr. 1, 1970, now U.S. Pat. No. 3,695,715, by the same inventor, there is disclosed an arrangement for propelling a projectile from a gun againsta rock wall, or the like. While detonable gases are specifically referred to, liquid or solid propellants may be used to equal or, in some environments, better advantage to propel the projectile out of the gun barrel at high velocity. The projectile impacts the rock and breaks the rock at and around the point of impact. Rubble thus produced is continually removed as additional projectiles are fired at spaced points on the rock wall. To facilitate the removal of rubble, and to minimize the dust in and around the area of excavation, water may be continually sprayed on the rock wall and rubble.

The present invention contemplates the same arrangement for excavation, but using a liquid (preferably water) jet to break up the rock. In a first embodiment, the liquid jet is produced by replacing the blunt nose concrete projectile of the prior arrangement with a projectile 10 having the shape shown in FIG. 1. That projectile is preferably made of two materials, a front cusp-shaped face of hardened steel, and the rest of plastic, although for simplicity it is shown as being made of all metal. The projectile is propelled through a gun barrel 11 upon the injection of two fluids, either gases or liquids, such as Nitric acid and .IP-4 jet engine fuel, behind the projectile in the firing chamber at the breach end of the gun (not shown). Alternatively, a solid propellant may be used. Thus, in general, the projectile is propelled by hot gases released by the combustion (detonation or conflagration) of gaseous, liquid or solid fuels in the firing chamber.

Shear pins or spring-loaded detents protruding from the gun barrel may be employed to hold the projectile in position until the hot gases of the combustion produce a predetermined minimum pressure, particularly when gaseous fuels are being used since they would be injected at some substantial pressure. Once the retaining the force of the shear pins or spring-loaded detents has been overcome, the projectile is propelled with a desired initial velocity V,,. Ultimately, the projectile would leave the gun barrel at a much lower velocity and strike the rock wall, but is insteadarrested near the end of the gun barrel, as will be more fully described hereinafter. While traveling in the gun barrel, the projectile will form a jet of liquid in front of it.

The manner in which the jet is formed, which is the subject matter of this invention, will now be described. A 4 lb. cylindrical projectile having a 4-inch diameter and an initial velocity of 5,000 ft/sec is assumed by way of example. The projectile is formed with an annular cusp 12 of a shape formed by revolving an arc (reclining on a side) about the axis of the projectile as shown. The leading portion of the axial projection is perferably of finite diameter, instead of a sharp, axial spike for practical reasons in producing and handling the projectile. Surface tension and expansion of the water as it leaves the projection would probably close any inner cavity after the jet is launched; if not, a hollow core in the jet would not be expected to have any deleterious effect.

The front outer edge of the projectile would have a very slight, but deliberate, chamfer (slope away from the barrel surface) to insure a thin layer of water is allowed to enter between the gun barrel and the projectile. For purposes of illustration, this chamfer is exaggerated in FIG. 2. This thin layer of water will lubricate the projectile and will transmit pressure from the inside curved surface of the projectile to the gun barrel, thereby providing support for the hoop tension in the projectile. Otherwise, the hoop tension would expand the leading edge of the projectile against the gun barrel and increase the frictional force opposing the motion of the projectile. An annular obturator may be added near the rear of the projectile, such as one or to O-rings of suitable resilient material in annular grooves on the projectile, to minimize gas blow-by. Two O-rings 13 and '14 are shown in the drawings.

Just prior to launching the projectile, a hollow cylinder 15 of liquid is injected into the gun barrel from the muzzle. A wetting agent may be added to the liquid to make sure this thin layer (about 0.05 inch thick) remains on the surface of the gun barrel for the period the projectile takes to scoop it up and form the jet. An exemplary system for injecting the liquid cylinder employs an annular nozzle 16 connected to an annular chamber 17 which is precharged with the liquid through a valve 18. Just prior to launching the projectile a compressed air valve 19 is opened to force an annular piston 20 toward the muzzle end of the chamber, thus injecting a measured quantity of liquid into the gun barrel in the form of a cylinder. Alternatively, injection of the liquid cylinder may be achieved by injecting metered quantities through tangential ports in the gun barrel. This would introduce a tangential component to the liquid velocity which will insure that the liquid will stay on the gun barrel until the projectile passes. The tangential component necessary to overcome gravity would be 2.3 ft/sec. If all the angular momentum of this tangential flow were converted to rotary motion of the jet produced, the jet would rotate at 130 revolutions per second, and that may cause the jet to break up prematurely. However, not all of the angular momentum will be converted, and a smaller tangential component of velocity is actuallY required because of the wetting qualities and surface tension of the liquid which will provide some of the force necessary to overcome gravity. Therefore, in practice the jet will rotate at less than 130 revolutions/second, and the jet will be less likely to break up prematurely.

A more practical alternative would be a dispenser momentarily inserted in the gun barrel between shots. The dispenser would spray the liquid, such as water to which a jelling agent has been added so that it will stick to the barrel surface. Any increase in the liquid viscosity produced by the agent would increase the stability of the high velocity jet formed.

As the projectile scoops up the liquid cylinder, and diverts its path inward and forward (in the direction of the projectiles motion), the liquid exerts a pressure on the projectile which is given by the following relation:

where R is the radius of curvature of the cusp arc, v is the tangential velocity of the liquid relative to the surface of the cusp, and p and t are respectively the density and thickness of fluid at that point. For the assumed parameters (namely a 4-inch diameter), the average radius of the cusp arc is of the order of 1 inch. The projectile velocity is assumed to be 5000 ft/sec while the liquid velocity can be called zero. For the parameters assumed, therefor, v is 5000 ft/sec. If the maximum desired pressure on the projectile is 30,000 psi, for example, then the thickness t of fluid is determined. For these parameters, it is about 0.10 inch.

Conservation of momentum and energy require that the velocity of the projectile and the velocity of the resultant jet follow respective curves 21 and 22 in the graph of FIG. 3, where v,, is initial velocity, M is mass of projectile, D is diameter of gun barrel, and M/rrDtp defines the distance the piston goes to pick up a mass of water equal to the piston mass. Here this distance is 200 inches. This is a valid approximation for maximum liquid pressure of 30,000 psi. It can be seen that the instantaneous velocity of the jet is always twice that of the projectile. When the velocity of the projectile has dropped to one half its initial velocity v a jet whose mass is 35 percent of the projectile mass has been launched. This jet has percent of the initial kinetic energy (KB) of the piston and has a range of velocities extending non-linearly from 2 v to v This analysis assumes incompressible inviscid liquid flow. As the projectile slows to 0.10 v it continues to form a liquid jet at the center of the cusp having an additional mass at percent that of the piston and carrying an additional 24 percent of the initial projectile energy. At this point vents allow the expanded gases to escape through a valve 23, and it would then be appropriate to stop the projectile by some mechanical means and return it to its initial position, e.g; an annular ring 24 compressed against and annular spring 25. The forces of the compressed spring will not be sufficient to return the projectile to its initial position, but the muzzle of the gun may be closed by a hatch (not shown) and compressed air may be introduced through the hatch. The vent valve 23 would also be closed during this period. Then the pressure of air is selected to be just enough to return the projectile to its initial position over the springloaded detents (if such are used).

The are of the cusp 12 has an increase in the radius of curvature both toward the axis and toward the outside periphery. Increase of the radius in this manner is necessary for two reasons. Toward the outside periphery one wishes to minimize the initial acceleration of the liquid which creates hoop tension in the projectile. There will be a thin film of liquid between the projectile and the gun barrel which will not only reduce friction and wear but will allow the gun barrel to provide radial support to the projectile as noted hereinbefore. Toward the axis it is desirable for the liquid to decompress and to attain as closely as possible an axial trajectory before the converging streams are combined into the forwardly propelled jet. This will prevent the jet from diverging before it can impact on the rock or at least minimize any tendency to diverge.

Although this embodiment limits the peak jet velocity to twice the velocity of the piston, it creates a jet the initial part of which has a velocity of 10,000 ft/sec. and a stagnation pressure of almost a million psi with internal pressures during projectile launching that do not exceed 30,000 psi. It delivers /1. of the projectile energy (i.e., over one million ft. lbs) at velocities above the initial velocity of the piston (i.e. above 5000 ft/sec.). Yet the design of the cusp is simple and not critical. Accordingly, the projectiles may be mass produced and, except for the cost of the metal, may be expendable. However since the projectile can be reused, it is preferred to arrest the projectile in the barrel as described for reuse. Alternatively, it may be feasible to allow the projectile to leave the barrel and to reclaim it from the rubble for reuse.

For even higher jet velocities, that are not limited to twice the projectile velocity, the embodiment of FIGS. 4a to 4d may be employed in which the projectile 30 is formed with an axial passage 31 that has a nonlinearly decreasing diameter from front to back as shown.

In any steady state jetting process, the velocity of the jet with reference to a stationary platform must always be larger than the phase velocity of the moving point where the converging fluid comes together. It is evident the limit of a high velocity jet is obtained when this velocity approaches infinity. If a scheme can be devised which will make a ring of liquid converge instantaneously along the axis, then the resultant infinite phase velocity can be reduced to whatever velocity is required to achieve any desired jet velocity. This theory is based on incompressible inviscid liquid. Because of the compressible nature of any liquid, a real velocity limit exists, but jets as high as 300,000 ft/sec have been experimentally generated.

The embodiment illustrated in FIGS. 4a to 4d will virtually achieve a collapsing ring of liquid with an infinite phase velocity. Liquid is injected in the form of a hollow frustrum of a cone 32 through an annular injection port 33 just before the projectile is launched, using an annular hydraulic piston arrangement 34 similar to that described with reference to FIG. 1 for the first embodiment. The projectile 30 then cuts off the injection port and gives the liquid the required dynamic motion. The successive FIGS. 4b, 0, and d show the progression of the implosion of the liquid as the wedge-like action of the projectile causes the liquid to converge on the axis virtually instantaneously.

It should be noted that the annular port shown will inject a liquid frustrum of a hollow cone only a cross section of which is shown by dashed lines in order to facilitate showing the imploding motion of the injected liquid.

It is apparent that the shape of the projectile 30 can be designed to provide any desired phaseevelocity. The term phase velocity" is used in the terminology of jets to signify the rate at which the point of convergence moves along the axis of the jet. As the half angle of the cone formed by the front of the converging liquid approaches zero, the phase velocity approaches infinity. Since there is no mass moving at this velocity, it is clear that the phase velocity is a virtual velocity. However, from the laws of conservation of mass and momentum, it can be shown that ajet must form whose velocity will be greater than the phase velocity, assuming an incompressible inviscid liquid. Again because of the compressible nature of any liquid, a. real velocity limit exists.

The passage 31 to the rear of the projectile is required to prevent interaction between the converged cone of liquid and the moving projectile. Otherwise, although a jet is propelled forward by the implosion of the liquid, the converged liquid of the cone will form a stationary slug with which the projectile will collide.

A coaxial rod 35 through the passage 31 seals the rear of the projectile 30 to cause the expanding hot gases to propel the projectile to the point where a jet has been formed. As the projectile advances further, the hot gases will expand through the passage to blow out the residual slug of liquid. Immediately following that additional liquid may be injected in front of the projectile to slow it down sufficiently for a spring system to bring it to rest. The projectile can then be slid back to its original position. To facilitate that, the end of the rod 35 is beveled and the rear of the passage 31 is provided with a curved surface: which will enable the end of the road to align itself with the axis of the projectile when it is slid back. Once the projectile has been slid over the end of the rod, compressed air may be used to seat the projectile in its original position. Up to that point, the projectile may be slid back manually.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art. Consequently, it is intended that the claims be interpreted to cover such modifications and variations.

What is claimed is:

1. In a system for producing a pulsed liquid jet of high dynamic pressure using a gun in which a cylindrical projectile is propelled through a barrel by hot gases released by the combustion of fuels in a firing chamber, the combination comprised. of

means for injecting a thin hollow liquid cylinder into a barrel of said gun just ahead of said projectile being propelled by hot gases, and

a shape on the leading end of :said projectile in the form of an annular cusp to scoop up said liquid and accelerate it inward toward the axis of said barrel and forward in the direction of motion of said projectile, as said projectile is propelled through said gun barrel, thus forcing a jet of liquid out of said barrel along the axis thereof with an instantaneous velocity nearly twice the instantaneous velocity of said projectile.

2. The combination of claim 1 wherein said projectile is chamfered around the outside circumference at the front end thereof to insure that a very thin layer of said liquid will pass between said gun barrel and said projectile to transmit pressure from said projectile to said gun barrel so that said gun barrel will provide radial support for said projectile.

3. In a system for producing a pulsed liquid jet of high dynamic pressure using a gun in which a cylindrical projectile is propelled through a barrel by hot gases released by the combustion of fuels in a firing chamber, the combination comprised of means for injecting a liquid ring in the shape of a hollow frustum of a cone into a barrel of said gun ahead of said projectile being propelled by hot gases, and

a shape for said projectile in the form of an axial passage through said projectile, said passage having a diameter which decreases from the front to the rear of said projectile starting with a diameter at the front substantially equal to the external diameter of said projectile so that said liquid is caused to con- 

1. In a system for producing a pulsed liquid jet of high dynamic pressure using a gun in which a cylindrical projectile is propelled through a barrel by hot gases released by the combustion of fuels in a firing chamber, the combination comprised of means for injecting a thin hollow liquid cylinder into a barrel of said gun just ahead of said projectile being propelled by hot gases, and a shape on the leading end of said projectile in the form of an annular cusp to scoop up said liquid and accelerate it inward toward the axis of said barrel and forward in the direction of motion of said projectile, as said projectile is propelled through said gun barrel, thus forcing a jet of liquid out of said barrel along the axis thereof with an instantaneous velocity nearly twice the instantaneous velocity of said projectile.
 2. The combination of claim 1 wherein said projectile is chamfered around the outside circumference at the front end thereof to insure that a very thin layer of said liquid will pass between said gun barrel and said projectile to transmit pressure from said projectile to said gun barrel so that said gun barrel will provide radial support for said projectile.
 3. In a system for producing a pulsed liquid jet of high dynamic pressure using a gun in which a cylindrical projectile is propelled through a barrel by hot gases released by the combustion of fuels in a firing chamber, the combination comprised of means for injecting a liquid ring in the shape of a hollow frustum of a cone into a barrel of said gun ahead of said projectile being propelled by hot gases, and a shape for said projectile in the form of an axial passage through said projectile, said passage having a diameter which decreases from the front to the rear of said projectile starting with a diameter at the front substantially equal to the external diameter of said projectile so that said liquid is caused to converge along said axis with a phase velocity greater than the projectile velocity, thereby producing an implosion of said liquid which in turn forces some of said liquid out of said barrel in front of said projectile as a high velocity jet. 